The Italian has taken responsibility for the "bad attitude" of les Parisiens after they drew 1-1 against Evian before being dumped out on penalties
Les Parisiens opened the scoring with Javier Pastore after eight minutes but that was the high point for the Ligue 1 table-toppers, as they allowed Saber Khlifa to make it 1-1 after 90 minutes prior to seeing Thiago Motta sent off in extra-time.
With the scores still deadlocked after the additional period, summer signings Zlatan Ibrahimovic and Thiago Silva both missed their spot-kicks in the shoot-out as Evian sealed an unlucky place in the semi-finals, leaving Ancelotti to rue his "worst" game in charge of the club.
"This is a disaster. This is the worst game in my reign, the worst," the Italian told Canal + after the match.
"I'm sorry, I'm very sorry. It's my responsibility. Our attitude was not good enough. When a team goes on a field with a bad attitude, it's the fault of the coach."
Ancelotti's side sit nine points ahead of Olympique de Marseille at the top of Ligue 1 with six games to this season.